Cordless telephones have become a common fixture in the modern household, to the extent that many consumers now have few, if any, conventional corded telephones. While the convenience, mobility, and high sound quality of cordless telephones have attracted many consumers, one of their drawbacks is that they consume more power than can be provided by a conventional telephone line. Consequently, modern cordless telephones must be plugged into a power outlet for operation.
One significant drawback of wall-powered cordless telephones is that such telephones commonly become inoperative during a power outage. If the telephone consumer does not also own a conventional corded telephone that operates on telephone line power, the consumer is then unable to place a telephone call reporting the power outage, or other emergencies. As a result, consumers must either keep an unwanted conventional telephone in service, or risk elimination of telephone services in the event of a power outage. Even if a consumer does keep a corded telephone in service, they will be inconvenienced by having to locate and utilize the corded telephone while power is out.
Some prior art cordless telephone designs have addressed this problem by including a rechargeable battery pack in the cordless telephone base unit, which can temporarily provide power to the base unit when the wall power supply fails. However, the effectiveness of this solution is limited by the significant power consumption of a typical cordless telephone system, resulting in limited battery life.
It is therefore an object of this invention to maximize cordless telephone utilization time following a power outage by placing the system into a sleep mode, during which power consumption is reduced.
It is another object of this invention to periodically check for incoming or outgoing calls such that the system retains functionality during the power outage.
It is yet another object of this invention to control the frequency with which the system checks for call activity based upon the power level remaining in the rechargeable batteries.
The invention involves a cordless telephone system, including a base unit and a portable unit, each capable of operating from a rechargeable battery pack as a power source. The base unit is further capable of operating on power supplied by an external source, such as a wall outlet and AC-to-DC converter.
In accordance with the method of the invention, the base unit detects when the external source of power fails. If the telephone system is not currently handling a call, the portable unit is placed into a mode in which its power consumption is reduced. The base unit is also placed into a mode of reduce power consumption, during which time calls cannot be processed. The length of the sleep period can be fixed at a predetermined interval. Alternatively, the period length can vary based on the amount of power remaining in the base unit battery. In one embodiment, the sleep period is interrupted immediately upon receipt of an incoming call on the telephone line to which the base unit is connected.
After sleeping for a period of time, the base unit circuits are awakened. The base unit then determines whether the telephone system is active. The telephone system will be deemed active if, for example, a telephone call is being placed by a user of the handset, or an incoming call is being received on the telephone line into which the base unit is connected. If the telephone system is active, the base unit handles the call.
Finally, when the telephone system is not active, and power is still not being supplied by the external power source, the base unit is placed back into the state of reduced power consumption, and the cycle is repeated.